1. Field of the Invention
This invention relates to a direct-acting table mechanism requiring precise control of position and high degree of straight motion for use in ultraprecision machine tools, measuring instruments, and other production systems, especially in surface finish grinding of semiconductor wafer substrates, grinding of magnetic heads and machining of lenses.
2. Description of the Related Art
In general, many table mechanisms requiring a function of positioning control use a screw feed system.
The screw feed system is designed: A feed screw is attached rotatably in its axial direction on supports, and nuts are attached to the table and screwed onto the feed screw. By turning the feed screw, the table is fed in its axial direction.
The screw feed system has some problems: Errors in mounting the feed screw and the table guide surface will affect accuracy of guide or the weight of screw will cause the screw to be deflected and disturbance exerted by twisting motion of the deflected screw will be transmitted to the table through the nuts to affect accuracy of movement. However, it is difficult to eliminate these problems. Especially in case of the workpiece formed of a hard brittle material such as the aforementioned semiconductor wafers, magnetic heads or lenses, if vibration occurs to the workpiece, fine vibration, for example, may cause chipping. To prevent this, the feed control of workpiece also requires a smooth constant-rate feed mechanism uninfluenced by irregularities of the sliding guide surface. Thus it is desirable to couple the nuts hydrostatically to the table so as to exclude the influence of errors in the screw feed system, but there has not been available any device satisfying high accuracy and rigidity.